Field of the Invention
The present invention relates to focus detection apparatuses and methods, and image capturing apparatuses.
Description of the Related Art
One known method for detecting a focus state of an imaging lens is an automatic focus detection method of an on-imaging plane phase difference type (on-imaging plane phase difference AF), in which pupil division focus detection is performed using a two-dimensional image sensor having microlenses formed on respective pixels. For example, Japanese Patent Laid-Open No. 2008-52009 describes a configuration in which, to perform pupil division focus detection, a plurality of photoelectric conversion portions in each pixel constituting an image sensor are partitioned, and the partitioned photoelectric conversion portions receive, via a microlens, light beams that have passed through different areas of a pupil of an imaging lens.
In on-imaging plane phase difference AF, a focus detection direction and a focus detection amount can be detected simultaneously based on a pair of signals obtained from focus detection pixels formed on the image sensor, and focus adjustment can be performed at high speed. Meanwhile, since focus detection is performed using a phase difference between optical images in on-imaging plane phase difference AF, there are cases where an aberration of an imaging lens for forming optical images may cause an error in the focus detection result, and methods for reducing such an error have been proposed.
Japanese Patent Laid-Open No. 2013-171251 discloses a method for correcting a focus detection error caused as a result of the shapes of a pair of optical images formed by a pair of light beams for focus detection not coinciding with each other when in an in-focus state due to an aberration in the optical system.
Japanese Patent Laid-Open No. 2014-222291 discloses a method for correcting a focus detection error in which correction is performed using a correction value corresponding to a combination of information regarding a state of an imaging lens, information regarding a state of an image sensor, and an image height.
However, mechanisms of a focus detection error caused by a chromatic aberration of magnification in on-imaging plane phase difference AF conventionally are not known in detail, and in particular, the fact that the aforementioned focus detection error is significantly affected by the characteristics of an image sensor is not known. Characteristics of an image sensor contained in a product considerably deviate from design values due to characteristic variation and manufacturing errors in image sensors. Since the correction value for a focus detection error caused by a chromatic aberration of magnification is typically calculated based on design values for an image sensor, a problem arises in that the accuracy of the correction value is low when in actual use.